Lamp having outer shell to radiate heat of light source

ABSTRACT

A lamp includes an outer shell having heat conductivity, a base provided in the outer shell, and a cover provided in the outer shell. The outer shell has a light source support, and a heat radiating surface exposed to the outside of the outer shell. The light source support is formed integral with the heat radiating surface. A light source is supported on the light source support. The light source is heated during lighting, and thermally connected to the light source support. The light source is covered with the cover.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.12/794,429, filed Jun. 4, 2010. U.S. application Ser. No. 12/794,429 isa continuation of U.S. application Ser. No. 11/399,492 filed Apr. 7,2006. U.S. application Ser. No. 11/399,492 claims priority to JapanesePatent Application No. 2005-112339 filed Apr. 8, 2005, Japanese PatentApplication No. 2005-221571 filed Jul. 29, 2005, Japanese PatentApplication No. 2005-221688 filed Jul. 29, 2005; and Japanese PatentApplication No. 2005-371406 filed. Dec. 26, 2005. The entire contents ofall of the applications mentioned above are incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a lamp using a semiconductor elementlike a light-emitting diode as a light source, and more particularly astructure for efficiently radiating the heat generated by a light sourceduring lighting of a lamp.

2. Description of the Related Art

A light-emitting diode is well known as a light source for a lampcompatible with an incandescent lamp. The output of the light-emittingdiode is lowered and the life is reduced, as the temperature isincreased. Therefore, it is necessary to control the increase of thetemperature of the light-emitting diode in the lamp using thelight-emitting diode as the light source.

For example, Jpn. Pat. Appln. KOKAI Publication No. 2001-243809discloses an LED lamp, which prevents overheat of a light-emitting diodeby increasing the heat radiation of the light-emitting diode. Theconventional LED lamp is provided with a spherical body, a metalsubstrate, and light-emitting diodes. The spherical body is composed ofa metallic radiator having a base at one end and an opening at the otherend, and a translucent cover. The metallic radiator has a shapespreading from one end to the other end like a bugle.

The metal substrate is fixed to the opening of the metallic radiatorthrough a high heat conductivity member having electrical insulation.The light-emitting diode is supported by the metal substrate and coveredby the translucent cover.

The heat generated by the light-emitting diode during lighting of theLED lamp is transmitted from the metal substrate to the metallicradiator through the high heat conductivity member. The heat transmittedto the metallic radiator is radiated to the atmosphere from theperipheral surface of the metallic radiator. This prevents overheat ofthe light-emitting diode, and increases the luminous efficiency of theLED lamp.

According to the LED lamp disclosed by the published Japanese patentapplications, the metallic radiator to radiate the heat of thelight-emitting diode and the metal substrate to mount the light-emittingdiode are different components. In this structure, though the metalsubstrate and the metallic radiator are connected through the high heatconductivity member, it is unavoidable to generate a thermal resistancein a joint of the metal substrate and the metallic radiator. Thus, theconduction of heat between the metal substrate and the metallic radiatordisturbed, and the heat of the light-emitting diode cannot beefficiently transmitted from the metal substrate to the metallicradiator. There is a point to be improved to control the temperatureincrease of the light-emitting diode.

Moreover, in the above-described LED lamp, a lighting circuit to lightthe light-emitting diode is an indispensable component. When thelighting circuit is incorporated in the LED lamp, it is requested thatthe size of the LED lamp is not increased by the lighting circuit. It isalso known that when the temperature of the lighting circuit isincreased, the reliability of the circuit operation is decreased and thelife is reduced. Therefore, it is essential to prevent overheat of thelighting circuit when the lighting circuit is incorporated in the LEDlamp.

The above-mentioned published Japanese patent applications do notdescribe about the lighting circuit. The LED lamps disclosed in theseapplications do not satisfy the demand for preventing the large size ofthe LED lamp and overheat of the lighting circuit.

BRIEF SUMMARY OF THE INVENTION

According to an embodiment of the present invention, there is provided alamp comprises; an outer shell with heat conductivity which includes alight source support, and a heat radiating surface exposed to theoutside of the outer shell, and the light source support formedintegrally with the heat radiating surface; a base which is provided inthe outer shell; a light source which is supported on the light sourcesupport, heated during lighting, and thermally connected to the lightsource support; and a cover which is provided in the outer shell so asto cover the light source.

According to an embodiment of the invention, the outer shell may be madeof copper with heat conductivity higher than iron-based metal, or acopper alloy composed mainly of copper. A light metal lighter thaniron-based metal such as aluminum, and light alloy may be used.

In an embodiment of the invention, the heat radiating surface of theouter shell may be knurled. This makes the heat radiating surface stainfinish, and increases the area of the heat radiating surface. Further,coating of a protection film is permitted to prevent rusting of the heatradiating surface of the outer shell. Particularly, if a blackprotection film is coated, the efficiency of heat radiation from theheat radiating surface to the atmosphere is increased.

In an embodiment of the invention, as a heat generating light source, itis desirable to use a semiconductor element, such as a light-emittingdiode which converts electrical energy into light. Instead of thelight-emitting diode, an electroluminescence element may be used. Thenumber of light source is one, but not limited to one. The light sourcemay be directly mounted on the light source support to facilitateconduction of heat to the light source support. The light source mayalso be mounted on a wiring board, and the wiring board may be thermallyconnected to the light source support.

In an embodiment of the invention, the cover is used to cover andprotect the light source. The cover may be shaped in a globe or a shade.If the cover is the globe, a light reflection film may be provided on apart of the inside surface of the globe. The cover may be shapedoptionally to diffuse or condense the light emitted from the lightsource. The cover may be either translucent or transparent. A lens tocondense or diffuse the light from the light source may be used as thecover.

According to an embodiment of the invention, the heat generated by thelight source during lighting is transmitted from the light sourcesupport to the heat radiating surface, and radiated to the outside ofthe lamp through the heat radiating surface. The light source support isformed integrally with the heat radiating surface, and there is nojoints disturbing heat conduction between the heat radiating surface andlight source support. Therefore, the heat conduction from the lightsource support to the heat radiating surface is good, and the heatgenerated from the light source is efficiently transferred to the heatradiating surface. As a result, the heat radiating performance of thelight source is increased, and overheat of the light source iseffectively prevented.

Additional objects and advantages of the invention will be set forth inthe description which follows, and in part will be obvious from thedescription, or may be learned by practice of the invention. The objectsand advantages of the invention may be realized and obtained by means ofthe instrumentalities and combinations particularly pointed outhereinafter.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate embodiments of the invention, andtogether with the general description given above and the detaileddescription of the embodiments given below, serve to explain theprinciples of the invention.

FIG. 1 is a perspective view of a lamp according to a first embodimentof the present invention;

FIG. 2 is a sectional view of the lamp according to the first embodimentof the present invention;

FIG. 3 is a sectional view of the first embodiment of the presentinvention, with a base, an outer shell and a translucent coverseparated;

FIG. 4 is a sectional view taken along line F4-F4 of FIG. 2;

FIG. 5 is a sectional view taken along line F5-F5 of FIG. 2;

FIG. 6 is a perspective view of a lamp according to a second embodimentof the present invention;

FIG. 7 is a sectional view of the lamp according to the secondembodiment of the present invention;

FIG. 8 is a sectional view of a lamp according to a third embodiment ofthe present invention;

FIG. 9 is a sectional view of a lamp according to a fourth embodiment ofthe present invention;

FIG. 10 is a sectional view of the lamp according to the fourthembodiment of the present invention, with a base, an outer shell and atranslucent cover separated;

FIG. 11 is a sectional view taken along line F11-F11 of FIG. 9;

FIG. 12 is a sectional view of a lamp according to a fifth embodiment ofthe present invention;

FIG. 13 is a sectional view of a lamp according to a sixth embodiment ofthe present invention;

FIG. 14 is a sectional view taken along line F14-F14 of FIG. 13;

FIG. 15 is a sectional view showing a positional relationship between alead wire and an insulating cylinder in a sixth embodiment of thepresent invention;

FIG. 16 is a front view showing a positional relationship between awiring board to support a light-emitting diode and a light sourcesupport in a sixth embodiment of the present invention;

FIG. 17 is a plan view of an insulating material used in the sixthembodiment of the present invention;

FIG. 18 is a sectional view taken along line F18-F18 of FIG. 17;

FIG. 19 is a sectional view taken along line F19-F19 of FIG. 17;

FIG. 20 is a perspective view of the insulating cylinder used in thesixth embodiment of the present invention;

FIG. 21 is a sectional view of a lamp according to a seventh embodimentof the present invention;

FIG. 22 is a sectional view showing a positional relationship among alight source support of an outer shell, a light source, a light sourcecover and a holder in the seventh embodiment of the present invention;

FIG. 23 is a sectional view showing a positional relationship among thelight source cover, the holder and a heat shielding cover in the seventhembodiment of the present invention;

FIG. 24 is an exploded perspective view showing a positionalrelationship among the outer shell, a heat conduction sheet and thelight source in the seventh embodiment of the present invention;

FIG. 25 is a perspective view of a separated light source cover of theseventh embodiment of the present invention;

FIG. 26 is a sectional view of a lamp according to an eighth embodimentof the present invention;

FIG. 27 is a plan view of the lamp according to the eighth embodiment ofthe present invention;

FIG. 28 is a sectional view of a lamp according to a ninth embodiment ofthe present invention; and

FIG. 29 is a plan view of the lamp according to the ninth embodiment ofthe present invention.

DETAILED DESCRIPTION OF THE INVENTION

A first embodiment of the present invention will be explainedhereinafter with reference to FIG. 1 to FIG. 5.

FIG. 1 and FIG. 2 show a bulb-type lamp 1 compatible with anincandescent lamp. The lamp 1 includes an outer shell 2, a light source3, a translucent cover 4, a lighting circuit 5, an insulating member 6,and a base 7.

The outer shell 2 is made of metallic material such as aluminum withexcellent heat conductivity. As shown in FIG. 2 and FIG. 3, the outershell 2 has a peripheral wall 8 and an end wall 9. The peripheral wall 8and the end wall 9 are formed integrally. The peripheral wall 8 iscylindrical. The outer circumference of the peripheral wall 8 is a heatradiating surface 10 exposed outside the lamp 1. The heat radiatingsurface 10 is tapered with the outside diameter decreased gradually fromone end to the other end along the axial direction of the peripheralwall 8.

The end wall 9 closes one end of the peripheral wall 8. The end wall 9forms a circular plate light source support 11. The light source support11 has a flat supporting surface 11 a exposed outside the outer shell 2.

In the first embodiment, the heat radiating surface 10 of the outershell 2 may be knurled and stain finished. This can increase the area ofthe heat radiating surface 10. The heat radiating surface 10 may becoated with a protection film to prevent rusting. If a black protectionfilm is coated, the efficiency of heat radiation from the heat radiatingsurface 10 to the atmosphere is increased.

As shown in FIG. 2 and FIG. 3, the outer shell 2 has a receptacle 12.The receptacle 12 is defined by a space surrounded by the peripheralwall 8 and the end wall 9, and positioned inside the heat radiatingsurface 10. The receptacle 12 has an open end 12 a opposite to the endwall 9. The open end 12 a is positioned at the other end of theperipheral wall 8.

The peripheral wall 8 has an inner peripheral surface exposed to thereceptacle 12. An engaging groove 8 a is formed on the inner peripheralsurface. The engaging groove 8 a is positioned at the open end 12 a ofthe receptacle 12, and continued in the circumferential direction of theperipheral wall 8. A recession 14 is formed in the outer circumferenceof the end wall 9. The recession 14 is circular surrounding the lightsource support 11, and opened outward of the outer shell 2.

As shown in FIG. 2 to FIG. 4, the light source support 11 has one screwhole 15 and a pair of through holes 16 a and 16 b. The screw hole 15 ispositioned at the center of the light source support 11. The throughholes 16 a and 16 b are positioned parallel to each other on both sidesof the screw hole 15. One end of the screw hole 15 and the ends of thethrough holes 16 a and 16 b are opened to the supporting surface 11 a ofthe light source support 11. The other end of the screw hole 15 and theother ends of the through holes 16 a and 16 b are opened to thereceptacle 12.

As shown in FIG. 4 and FIG. 5, the light source 3 includes fourlight-emitting diodes 18 shaped like a chip, for example. Thelight-emitting diodes 18 are an example of a point source of light, andmounted in two lines on a circular wiring board 19. The wiring board 19has an insulating substrate 20. The insulating substrate 20 has a firstsurface 20 a and a second surface 20 b. The second surface 20 b ispositioned on the opposite side of the first surface 20 a.

A pattern layer 21 and a resist layer 22 are stacked on the firstsurface 20 a of the insulating substrate 20. The pattern layer 21 ismade of metal foil such as copper. The resist layer 22 covers thepattern layer 21. A thermal diffusion layer 23 and a resist layer 24 arestacked on the second surface 20 b of the insulating substrate 20. Thethermal diffusion layer 23 is made of metal foil with excellent heatconductivity such as an alloy. The thermal diffusion layer 23 is thickerthan the pattern layer 21 to ensure heat capacity. As shown in FIG. 5,the thermal diffusion layer 23 is divided into four areas 23 a, 23 b, 23c and 23 d. The areas 23 a, 23 b, 23 c and 23 d are separated, andcorrespond to the mounting positions of the light-emitting diodes 18.The resist layer 24 covers the thermal diffusion layer 23. Thelight-emitting diodes 18 are mounted on the first surface 20 a of theinsulating substrate 20, and electrically connected to the pattern layer21.

As the wiring board 19, a pattern layer, a thermal diffusion layer and aresist layer may be stacked on a metal substrate with excellent heatconductivity. However, considering the cost, it is desirable to use aresin substrate made of epoxy resin mixed with glass powder as theinsulating substrate 20, and to stack a pattern layer, a thermaldiffusion layer and a resist layer on the resin substrate.

The wiring board 19 is stacked on the light source support 11 with thethermal diffusion layer 23 faced to the supporting surface 11 a of thelight source support 11. The wiring board 19 is fixed to the lightsource support 11 through a screw 26. The screw 26 is inserted into thescrew hole 15 penetrating the center of the wiring board 19. With thisinsertion of the screw, the wiring board 19 is fixed tightly to thesupporting surface 11 a of the light source support 11, and the wiringboard 19 is thermally connected to the light source support 11.

Therefore, the heat generated by the light-emitting diode 18 istransmitted from the insulating substrate 20 to the thermal diffusionlayer 23, and diffused widely to every corner of the thermal diffusionlayer 23. The heat diffused to the heat diffusion layer 23 istransmitted to the light source support 11 through the resist layer 24.

According to the first embodiment, a heat conduction path from thewiring board 19 to the supporting surface 11 a is formed in the lightsource support 11 of the outer shell 2. To control the thermalresistance of the heat conduction path, it is desirable to fill aheat-conducting substance consisting mainly of silicon, such as greasebetween the wiring board 19 and the supporting surface 11 a.

The translucent cover 4 is a globe made of synthetic resin, for example,and is formed spherical having an opening 4 a at one end. Thetranslucent cover 4 is held by the outer shell 2 by fitting an edge 4 bdefining the opening 4 a into the recession 14 of the outer shell 2. Thetranslucent cover 4 hides the light source support 11, light-emittingdiodes 18 and wiring board 19. Therefore, the light-emitting diodes 18are faced to the inside surface of the translucent cover 4.

The lighting circuit 5 is used to light up the light-emitting diodes 18,and unified as one module. As shown in FIG. 2, the lighting circuit 5has a wiring board 28 and circuit components 29. The wiring board 28 hasa first surface 28 a and a second surface 28 b positioned on theopposite side of the first surface 28 a. The circuit components 29 aremounted on the first surface 28 a of the wiring board 28. The circuitcomponents 29 have lead terminals. The lead terminals are soldered toconductor patterns (not shown) printed on the wiring bard 28,penetrating through the wiring board 28.

The lighting circuit is housed in the receptacle 12 of the outer shell2. The lighting circuit 5 has lead wires 30 a and 30 b electricallyconnected to the light-emitting diodes 18, and a lead wire (not shown)electrically connected to the base 7. The lead wires 30 a and 30 b areled to the wiring board 19, penetrating through the through holes 16 aand 16 b formed on the end wall 9. The lead wires 30 a and 30 b areconnected to the pattern layer 21 of the wiring board 19 by means ofsoldering. Therefore, as shown in FIG. 2, when the translucent cover 4is directed to the lamp 1 located on the outer shell 2, the lightingcircuit 5 is suspended from the light support 11 by the lead wires 30 aand 30 b.

The insulating member 6 is an example of insulating layer forelectrically insulating between the outer shell 2 and the lightingcircuit 5. The insulating member 6 is a molding using synthetic resinmaterial, such as polybutylene terephthalate. As shown in FIG. 2, theinsulating member 6 is cup-shaped having a cylindrical peripheral wall32 a and a closed wall 32 b closing one end of the peripheral wall 32 a.The closed wall 32 b has a pair of through holes 33 a and 33 b to passthe lead wires 30 a and 30 b. The axial length A of the insulatingmember 6 is shorter than the axial length B from the light sourcesupport 11 to the engaging groove 8 a of the outer shell 2.

The insulating member 6 is fit in the receptacle 12 through the open end12 a. Therefore, the peripheral wall 32 a of the insulating member 6covers the internal circumference of the peripheral wall 8 of the outershell 2, and the closed wall 32 b of the insulating member 6 covers theinside surface of the end wall 9 of the outer shell 2. The insulatingmember 6 partitions the outer shell 2 and the lighting circuit 5.

The base 7 is used to supply a current to the lighting circuit 5. Thebase 7 has a metal base shell 35, and a connecting member 36 fixed tothe base shell 35. The base shell 35 is removably screwed into a lampsocket of a not-shown light fixture. The connecting member 36 is amolding using synthetic resin material, such as polybutyleneterephthalate, and has electrical insulation. The connecting member 36has a peripheral surface 36 a, which is formed to have a cylindricalhollow and curved circularly.

As shown in FIG. 2, the connecting member 36 has a distal end 37 to fitin the inside of the open end 12 a of the receptacle 12. The distal end37 has an engaging projection 38 on the peripheral surface. The engagingprojection 38 engages with the engaging groove 8 a when the distal end37 is fit inside the open end 12 a. By this engagement, the outer shell2 and the base 7 are coaxially connected. The connecting member 36 isinterposed between the base shell 35 and the outer shell 2, insulatingthem electrically and thermally.

In the state that the connecting member 36 is connected to the outershell 2, the peripheral surface 36 a of the connecting member 36 iscontinued to the heat radiating surface 10 of the outer shell 2. A step39 is formed in the base of the distal end 37. The step 39 has a flatsurface, which is continued in the circumferential direction of theconnecting member 36, and extending in the radial direction of theconnecting member 36. The step 39 butts against the open end 12 a, whenthe distal end 37 of the connecting member 36 is inserted into the openend 12 a of the receptacle 12. This controls the insertion depth of thedistal end 37 of the connecting member 36 into the receptacle 12.

As the insertion depth of the distal end 37 is controlled, a space S isgenerated between the distal end 37 of the connecting member 36 and theperipheral wall 32 a of the insulating member 6. The existence of thespace S prevents interference of the distal end 37 with the insulatingmember 6 before the engaging projection 38 engages with the engaginggroove 8 a. In other words, Failure in engagement between the engagingprojection 38 and the engaging groove 8 a caused by a dimensionaltolerance of the connecting member 36 and outer shell 2 is prevented.Therefore, the base 7 can be surely connected to the open end 12 a ofthe receptacle 12.

In the lamp 1 of the first embodiment, when the lamp 1 is lit, thelight-emitting diodes 18 are heated. The light-emitting diodes 18 arecooled in the following process, in addition to the cooling byconviction of the air generated within the translucent cover 4.

The heat of the light-emitting diodes 18 are transmitted to the lightsource support 11 of the outer shell 2 through the wiring board 19. Theheat transmitted to the light source support 11 is transmitted from theend wall 9 to the heat radiating surface 10 through the peripheral wall8, and radiated to the outside of the lamp 1 through the heat radiatingsurface 10.

The light source support 11 receiving the heat of the light-emittingdiodes 18 is formed integrally with the peripheral wall 8 having theheat radiating surface 10. There is no joint to disturb the conductionof heat on the heat conduction path from the light source support 11 tothe heat radiating surface 10, and the thermal resistance of the heatconduction path is decreased. Therefore, the heat of the light-emittingdiodes 18 transmitted to the light source support 11 can be efficientlyescaped to the heat radiating surface 10.

In addition, in the first embodiment, the circular recession 14surrounding the light source support 11 is formed in the end wall 9 ofthe outer shell 2, and the recession 14 is opened outward of the outershell 2. The existence of the recession 14 increases the surface area ofthe outer shell 2, and increases the amount of heat radiation from theouter shell 2 though the shape of the outer shell 2 is restricted by theappearance of the lamp 1.

As a result, the cooling performance of the light-emitting diodes 18 isincreased, and overheat of the light-emitting diodes 18 is prevented.Therefore, the decrease of the light-emitting efficiency of thelight-emitting diodes 18 can be controlled, and the life of thelight-emitting diodes 18 can be made long.

Moreover, the light-emitting diodes 18 are mounted on the wiring board19 having the thermal diffusion layer 23, and the heat generated by thelight-emitting diodes 18 are diffused to every corner of the wiringboard 19 through the thermal diffusion layer 23 of the wiring board 19.Therefore, the heat of the light-emitting diodes 18 can be transmittedfrom a wide area of the wiring board 19 to the light source support 11.This improves the heat conduction from the light-emitting diodes 18 tothe light source support 11, and increases the cooling performance ofthe light-emitting diodes 18.

Further, the lamp 1 of the first embodiment has the receptacle 12 tocontain the lighting circuit 5 inside the outer shell 2. This eliminatesthe necessity of arranging the lighting circuit 5 and outer shell 2 inthe axial direction of the lamp 1. Therefore, the length of the lamp 1in the axial direction can be reduced, and the compact lamp 1 can beprovided.

The lighting circuit 5 contained in the receptacle 12 is electricallyinsulated from the outer shell 2 through the insulating member 6.Therefore, the lighting circuit 5 can be incorporated in the outer shell2, while the outer shell 2 is made of metal to increase the heatradiation performance.

The cup-shaped insulating member 6 for electrically insulating the outershell 2 and the lighting circuit 5 is a synthetic resin molding with theheat conductivity lower than the outer shell 2. Therefore the insulatingmember 6 can thermally shield the lighting circuit 5 from the outershell 2, and prevents conduction of the heat of the light-emittingdiodes 18 to the lighting circuit 5 through the outer shell 2. As aresult, the lighting circuit 5 is protected from the heat of thelight-emitting diodes 18. This prevents a malfunction of the lightingcircuit 5, and makes the life of the lighting circuit 5 long.

The receptacle 12 containing the lighting circuit 5 is surrounded by theperipheral wall 8 and the end wall 9 of the outer shell 2, and the openend 12 a of the receptacle 12 is closed by the base 7. In other words,the lighting circuit 5 is contained in a space portioned by the outershell 2 and base 7. The air outside the lamp 1 does not flow in thisspace. This prevents adhesion of dust in the air to the lighting circuit5 causing a tracking phenomenon.

FIG. 6 and FIG. 7 show a second embodiment of the invention.

The second embodiment is different from the first embodiment in theouter shell 2 and translucent cover 4. The other components of the lamp1 and technical effects are the same as those of the first embodiment.Therefore, the same components as those of the first embodiment aregiven same reference numerals, and explanation of these components willbe omitted.

As shown in FIG. 6 and FIG. 7, in the lamp 1 according to the secondembodiment, the outside diameter of the peripheral wall 8 of the outer,shell 2 is constant except the end portion adjacent to the open end 12 aof the receptacle 12 of the outer shell 2. Therefore, the outer shell 2is shaped like a straight cylinder.

A globe as the translucent cover 4 has a reflection portion 41 a and aprojection portion 41 b. The reflection portion 41 a has an opening 42 aopened to the light source support 11, and an edge 42 b defining theopening 42 a. The edge 42 b is fit in the recession 14 of the outershell 2. The reflection portion 41 a is tapered to increase the diametergradually from the edge 42 b. A light reflection film 43 is stacked onthe inside surface of the reflection portion 41 a.

The projection portion 41 b is formed integrally with the reflectionportion 41 a so as to continue to the reflection portion 41 a. Theprojection portion 41 b is faced to the light reflection film 43 andlight-emitting diodes 18.

With the translucent cover 4 formed as described above, a part of thelight from the light-emitting diodes 18 can be reflected to theprojection portion 41 b by using the light reflection film 43.Therefore, most of the light from the light-emitting diodes 18 can becondensed by the projection portion 41 b, and projected to the outsideof the lamp 1.

As shown in FIG. 7, the outer shell 2 has a stopper 45 at the cornerdefined by the peripheral wall 8 and the end wall 9. The stopper 45 isformed circular, projecting from the inside surface of the peripheralwall 8 and continuing to the inner circumference of the peripheral wall8. The stopper 45 is not limited to the circular form. For example,stoppers projecting from the inner circumference of the peripheral wall8 may be arranged with intervals in the circumferential direction of theperipheral wall 8.

The inside diameter of the stopper 45 is smaller than the outsidediameter of the closed wall 32 b of the insulating member 6. Therefore,the stopper 45 is interposed between the end wall 9 and the closed wall32 b of the insulating member 6, even in the state that the insulatingmember 6 is fit in the receptacle 12 of the outer shell 2. As a result,the light source support 11 on the end wall 9 is separated from theinsulating member 6, and a gap 46 is provided therebetween.

According to the lamp 1 of the second embodiment, the existence of thegap 46 keeps the light source support 11 to receive the heat of thelight-emitting diodes 18 non-contacting with the insulating member 6.The gap 46 functions as a heat shielding space to prevent conduction ofheat from the light source support 11 to the insulating member 6, andthe heat of the light-emitting diodes 18 are difficult to transmitdirectly from the light source support 11 to the insulating member 6.

Therefore, though the lighting circuit 5 is contained in the outer shell2 which receives and radiates the heat of the light-emitting diodes 18,the influence of heat to the lighting circuit 5 can be minimized. Thisprevents a malfunction of the lighting circuit 5, and makes the life ofthe lighting circuit 5 long.

FIG. 8 shows a third embodiment of the invention.

The third embodiment is different from the first embodiment in themethod of fixing the translucent cover 4 to the outer shell 2. The othercomponents of the lamp 1 and technical effects are the same as those ofthe first embodiment. Therefore, the same components as those of thefirst embodiment are given same reference numerals, and explanation ofthese components will be omitted.

As shown in FIG. 8, the edge 4 b of the translucent cover 4 is fixed tothe recession 14 of the outer shell 2 through a silicon-based adhesive51. The adhesive 51 is filled in the recession 14. The recession 14 isformed surrounding the light source support 11, and caved in toward thebase 7 from the supporting surface 11 a to fix the wiring board 19.Therefore, the adhesive 51 is provided at the position displaced to thebase 7 from the light-emitting diodes 18 on the wiring board 19.

According to the lamp 1 of the third embodiment, the adhesive 51 to fixthe translucent cover 4 to the outer shell 2 is filled in the recession14 caved in from the supporting surface 11 a of the light source support11. Therefore, the light from the light-emitting diodes 18 is difficultto apply directly to the adhesive 51. This prevents deterioration of theadhesive 51, even if the light from the light-emitting diodes 18includes an ultraviolet ray. Therefore, the translucent cover 4 issecurely fixed to the outer shell 2 for a long period.

FIG. 9 to FIG. 11 shows a fourth embodiment of the invention.

The fourth embodiment is different from the third embodiment in theshape of the light support 11 of the outer shell 2. The other componentsof the lamp 1 and technical effects are the same as those of the thirdembodiment. Therefore, the same components as those of the thirdembodiment are given same reference numerals, and explanation of thesecomponents will be omitted.

As shown in FIG. 9 to FIG. 11, the end wall 9 of the outer shell 2 has aprojection 61 projecting from the light source support 11 to thetranslucent cover 4. The projection 61 is formed circular one sizesmaller than the light source support 11. The projection 61 is formedintegrally with the end wall 9, and surrounded coaxially by therecession 14 to fix the translucent cover 4. Therefore, one step 62 isformed between the projection 61 and light source support 11. The step62 is circular continuing to the circumferential direction of theprojection 61.

A flat supporting surface 63 is formed at the end of the projection 61.The supporting surface 63 is placed inside the translucent cover 4 moreclosely to the center than the end wall 9 of the outer shell 2.Therefore, the supporting surface 63 is farther from the recession 14 bythe distance equivalent to the height of the projection 61.

In the fourth embodiment, the wiring board 19 with the light-emittingdiodes 18 mounted is fixed to the center of the supporting surface 63through the screw 26. The wiring board 19 is thermally connected to thesupporting surface 63. The screw hole 15 and through holes 16 a/16 b areopened to the supporting surface 63, penetrating through the projection61.

According to the lamp 1 of the fourth embodiment, the projection 61projecting to the translucent cover 4 is formed in the light support 11of the outer shell 2, and the wiring board 19 having the light-emittingdiodes 18 is fixed to the end surface 63 of the projection 61.Therefore, the light-emitting diodes 18 are displaced to be inside thetranslucent cover 4 more closely to the center than the end wall 9 ofthe outer shell 2. This efficiently guides the light from thelight-emitting diodes 18 to the inside of the translucent cover 4, andpermits radiation of the light from here to the outside of thetranslucent cover 4.

Further, the existence of the projection 61 increases the surface areaand heat capacity of the light source support 11. This increases theamount of heat radiation from the outer shell 2, though the shape of theouter shell 2 is restricted by the appearance of the lamp 1. As aresult, the cooling performance of the light-emitting diodes 18 isincreased, overheat of the light-emitting diodes 18 is prevented, andthe life of the light-emitting diodes 18 can be made long.

The light-emitting diodes 18 are farther from the adhesive 51 filled inthe recession 14 by the distance equivalent to the height of theprojection 61. In other words, the light from the light-emitting diodes18 to the recession 14 is blocked by the outer circumference of theprojection 61, and the light from the light-emitting diodes 18 isdifficult to apply directly to the adhesive 51.

This prevents deterioration of the adhesive 51, even if the light fromthe light-emitting diodes 18 includes an ultraviolet ray. Therefore, thetranslucent cover 4 is securely fixed to the outer shell 2 for a longperiod.

FIG. 12 shows a fifth embodiment of the invention.

The fifth embodiment is different from the second embodiment in theshape of the light source support 11 of the outer shell 2. The othercomponents of the lamp 1 and technical effects are the same as those ofthe second embodiment. Therefore, the same components as those of thesecond embodiment are given same reference numerals, and explanation ofthese components will be omitted.

As shown in FIG. 12, the end wall 9 of the outer shell 2 has aprojection 71 projecting from the light source support 11 to thetranslucent cover 4. The projection 71 is formed circular one sizesmaller than the light source support 11. The projection 71 is formedintegrally with the end wall 9, and surrounded coaxially by therecession 14 to fix the translucent cover 4. Therefore, one step 72 isformed between the projection 71 and light source support 11. The step72 is circular continuing to the circumferential direction of theprojection 71.

A flat supporting surface 73 is formed at the end of the projection 71.The supporting surface 73 is placed inside the reflection portion 41 aof the translucent cover 4 more closely to the center than the end wall9 of the outer shell 2. Therefore, the supporting surface 73 is fartherfrom the recession 14 by the distance equivalent to the height of theprojection 71.

In the fifth embodiment, the wiring board 19 with the light-emittingdiodes 18 mounted is fixed to the center of the supporting surface 73through the screw 26. The wiring board 19 is thermally connected to thesupporting surface 73. The screw hole 15 and through holes 16 a/16 b areopened to the supporting surface 73, penetrating through the projection71.

According to the lamp 1 of the fifth embodiment, the light-emittingdiodes 18 are displaced to be inside the reflection portion 41 a of thetranslucent cover 4 more closely to the center than the end wall 9 ofthe outer shell 2. This efficiently guides the light from thelight-emitting diodes 18 to the inside of the translucent cover 4.Therefore, the light from the light-emitting diodes 18 can be reflectedto the projection portion 41 b through the light reflection film 43, andradiated from the projection portion 41 b to the outside of thetranslucent cover 4.

Further, the existence of the projection 71 increases the surface areaand heat capacity of the light source support 11. This increases theamount of heat radiation from the outer shell 2, though the shape of theouter shell 2 is restricted by the appearance of the lamp 1. As aresult, the cooling performance of the light-emitting diodes 18 isincreased, overheat of the light-emitting diodes 18 is prevented, andthe life of the light-emitting diodes 18 can be made long. FIG. 13 toFIG. 20 shows a sixth embodiment of the invention.

The sixth embodiment is different from the first embodiment in themethod of supporting the lighting circuit 5 to the receptacle 12 of theouter shell 2. The other components of the lamp 1 and technical effectsare the same as those of the first embodiment. Therefore, the samecomponents as those of the first embodiment are given same referencenumerals, and explanation of these components will be omitted.

As shown in FIG. 13 and FIG. 14, the wiring board 28 constituting thelighting circuit 5 is formed rectangular in the axial direction of theperipheral wall 8 of the outer shell 2. The wiring board 28 has first tofourth edges 81 a, 81 b, 81 c and 81 d. The first and second edges 81 aand 81 b are extended along the axial direction of the peripheral wall8. The third and fourth edges 81 c and 81 d are extended along theradial direction of the peripheral wall 8. The third edge 81 c buttsagainst the closed wall 32 b of the insulating member 6. The fourth edge81 d faces to the base 7.

A first engaging part 82 a is formed at the corner of the wiring board28 defined by the first edge 81 a and fourth edge 81 d. Similarly, asecond engaging part 82 b is formed at the corner of the wiring board 28defined by the second edge 81 b and fourth edge 81 d. The first andsecond engaging parts 82 a and 82 b are formed by notching two cornersof the wiring board 28 rectangularly. The first and second engagingparts 82 a and 82 b are not limited to the notching. For example,projections projecting to the peripheral wall 8 may be provided at twocorners of the wiring board 28, and these projections may be used as thefirst and second engaging parts 82 a and 82. Or, two corners themselvesof the wiring board 28 may be used as the first and second engagingparts 82 a and 82 b.

The wiring board 28 projects from the open end 12 a of the receptacle 12to the inside of the connecting member 36 of the base 7. In other words,the wiring board 28 extends over the outer shell 2 and the base 7, andthe fourth edge 81 d is placed inside the connecting member 36.

As shown in FIG. 13, the circuit components 29 composing the lightingcircuit 5 include a condenser 83. The condenser 83 is weak to heat, andhas a characteristic that the life is reduced when heated. The condenser83 is mounted at the end portion of the first surface 28 a of the wiringboard 28 adjacent to the fourth edge 81 d by means of soldering.

Further, the lead terminal of each of the circuit components 29 projectsfrom the second surface 28 b of the wiring board 28, penetrating thewiring board 28. Chip components 84 are mounted on the second surface 28b.

As shown in FIG. 14, a pair of stoppers 85 a and 85 b is formed on theinternal circumference of the connecting member 36. The stoppers 85 aand 85 b project from the internal circumference of the connectingmember 36 so as to correspond to the first and second engaging parts 82a and 82 b of the wiring board 28. The stoppers 85 a and 85 b contactthe first and second engaging parts 82 a and 82 b of the wiring board28. Therefore, the wiring board 28 is held between the stoppers 85 a and85 b of the base 7 and the end wall 9 of the outer shell 2.

As shown in FIG. 17 to FIG. 19, a pair of guides 87 a and 87 b is formedintegrally on the internal circumference of the peripheral wall 32 a ofthe insulating member 6. The guides 87 a and 87 b are faced to eachother in the radial direction of the peripheral wall 32 a, and projectedfrom the internal circumference of the peripheral wall 32 a. Further,the guides 87 a and 87 b are extended along the axial direction of theperipheral wall 32 a.

An engaging groove 88 is formed in the guides 87 a and 87 b. The firstand second edges 81 a and 81 b are fit slidable in the engaging grooves88. The engaging grooves 88 are extended linearly along the axialdirection of the peripheral wall 32 a. One ends of the engaging grooves88 are closed by the closed wall 32 b of the insulating member 6. Theother ends of the engaging grooves 88 are opened to the other end of theperipheral wall 32 a.

When installing the lighting circuit 5 in the receptacle 12, insert thewiring board 28 into the inside of the peripheral wall 32 a of theinsulating member 6 by setting the third edge 81 c of the wiring board28 to the front. Insertion of the wiring board 28 is performed, whileinserting the first and second edges 81 a and 81 b of the wiring board28 into the engaging grooves 88. When inserting the wiring board 28 intothe inside of the peripheral wall 32 a, the third edge 81 c of thewiring board 28 butts against the closed wall 32 b of the insulatingmember 6. This determines the insertion depth of the wiring board 28into the insulating member 6 without taking special care. This improvesthe workability when installing the lighting circuit 5 in the receptacle12.

After inserting the wiring board 28 into the inside of the peripheralwall 32 a of the insulating member 6, connect the connecting member 36of the base 7 to the open end 12 of the outer shell 2. By thisconnection, the stoppers 85 a and 85 b of the connecting member 36contact the first and second engaging parts 82 a and 82 b of the wiringboard 28. Therefore, the wiring board 28 is held between the end wall 11of the outer shell 2 and the stoppers 85 a and 85 b, holding thelighting circuit 5 not to move in the axial direction of the peripheralwall 8. As the first and second edges 81 a and 81 b of the wiring board28 are fit in the engaging grooves 88 of the insulating member 6, thelighting circuit 5 is held not to move in the circumferential directionof the peripheral wall 8. Further, by intensifying the fitting of thefirst edge 81 a of the wiring board 28 in the engaging groove 88, thelighting circuit 5 can be held not to move in the peripheral directionof the peripheral wall 8 only by fitting the first edge 81 a in theengaging groove 88.

Therefore, the lighting circuit 5 is held unmovable in the receptacle 12of the outer shell 2.

As shown in FIG. 13, the wiring board 28 of the lighting circuit 5partitions the inside of the peripheral wall 32 a of the insulatingmember 6 into two areas 89 a and 89 b along the radial direction. Theareas 89 a and 89 b are opened to a space 90 inside the base 7, andconnected with each other through the space 90.

The first and second surfaces 28 a and 28 b of the wiring board 28 arenot directed to the light source support 11 which receives the heat ofthe light-emitting diodes 18, and faced to the peripheral wall 32 a ofthe insulating member 6. Therefore, the soldered parts of the leadterminals of the circuit components 29 to the wiring board 28 areseparated away from the closed wall 32 b of the insulating member 6contacting the light source support 11, preventing the influence of heatto the soldered parts.

Further, the condenser 83 adjacent to the fourth edge 81 d of the wiringboard 28 is placed in the space 90 inside the base 7, and separated awayfrom the light source support 11 which receives the heat of thelight-emitting diodes 18. Therefore, the condenser 83 is difficult to beinfluenced by the heat of the light-emitting diodes 18, and increased inthe durability.

In addition, as a part of the lighting circuit 5 is placed in the space90 inside the base 7, the lengths of the insulating member 6 and theouter shell 2 in the axial direction can be reduced. This isadvantageous to make the lamp 1 compact. However, when the length of theouter shell 2 in the axial direction is reduced, the area of the heatradiating surface 10 is decreased. To solve this problem, increase theoutside diameter of the outer shell 2 to compensate for the decrease ofthe area of the heat radiating surface 10.

As shown in FIG. 13 and FIG. 16, the circuit components 29 mounted onthe first surface 28 a of the wiring board 28 are higher than the chipcomponents 84 mounted on the second surface 28 b. Therefore, the wiringboard 28 of this embodiment is offset to the center line X1 of the lamp1, so that the area 89 a between the first surface 28 a and theperipheral wall 32 a of the insulating member 6 becomes larger than thearea 89 b between the second surface 28 b and the peripheral wall 32 aof the insulating member 6.

As a result, the high circuit components 29 can be separated as far aspossible from the peripheral wall 8 of the outer shell 2, and thecircuit components 29 are difficult to be influenced by the heat of thelight-emitting diodes 18 transmitted to the peripheral wall 8. At thesame time, a certain capacity can be ensured in the area 89 b betweenthe second surface 28 b and the peripheral wall 8 of the outer shell 2.Therefore, even if the lead terminals of the circuit components 29 areprojected to the area 89 b from the second surface 28 b of the wiringbard 28, the lead terminals are difficult to be influenced by the heatof the light-emitting diodes 18 transmitted to the peripheral wall 8.This prevents overheat of the part where the lead terminals are solderedto the wiring board 28.

According to the lamp 1 of the sixth embodiment, the wiring board 28 ofthe lighting circuit 5 is contained in the receptacle 12 of the outershell 2 in the state that the first and second surfaces 28 a and 28 bare faced to the internal circumference of the peripheral wall 32 a ofthe insulating member 6. Therefore, the first or second surface 28 a or28 b of the wiring board 28 is not faced to the closed wall 32 b of theinsulating member 6.

Therefore, a substantially enclosed space is not formed between thewiring board 28 and closed wall 32 b, and the heat generated by thelighting circuit 5 or the heat of the light-emitting diodes 18transmitted to the light source support 11 is difficult to stay at theend portion of the receptacle 12 adjacent to the light source support11. This prevents overheat of the light source support 11, and isadvantageous to increase the cooling performance of the light-emittingdiodes 18.

Further, the wiring board 28 extends over the outer shell 2 and the base7, and the size of the wiring board 28 is not restricted by the insidediameter of the insulating member 6. This increases the flexibility ofdetermining the size of the wiring board 28 and laying out the circuitparts 29 on the wiring board 28, and makes it easy to design thelighting circuit 5.

The sixth embodiment shows a structure to prevent a short circuitbetween the outer shell 2 and lead wires 30 a and 30 b.

As shown in FIG. 14 and FIG. 15, a pair of through holes 16 a and 16 bformed in the light source support 11 has a small diameter part 91, alarge diameter part 92 and a step 93. The step 93 is positioned in theboundary between the small diameter part 91 and large diameter part 92.

An insulating cylinder 94 is fit in the through holes 16 a and 16 b. Theinsulating cylinder 94 is made of synthetic resin material havingelectric insulation such as polybutylene terephthalate. The insulatingcylinder 94 extends over the small diameter part 91 and large diameterpart 92, covering the inside surfaces of the through holes 16 a and 16b.

The insulating cylinder 94 has an insertion hole 95 to pass the leadwires 30 a and 30 b. The insertion hole 95 extends over the throughholes 33 a and 33 b of the insulating member 6. As shown in FIG. 15, anopen edge adjacent to the through holes 33 a and 33 b of the insertionhole 95 is expanded in the diameter by chamfering. This prevents thelead wires 30 a and 30 b from being caught by the open edge of theinsertion hole 95 when the lead wires 30 a and 30 b are guided from thethrough holes 33 a and 33 b to the insertion hole 95.

The insulating cylinder 94 is fit in the through holes 16 a and 16 bfrom the supporting surface 11 a of the light source support 11. Byfixing the wiring board 28 onto the supporting surface 11 a, theinsulating cylinder 94 is held between the wiring board 28 and the step93 of the through holes 16 a and 16 b, and the insulating cylinder 94 isheld by the light source support 11. Therefore, it is unnecessary tobond the insulating cylinder 94 to the light source support 11. Thismakes it easy to assemble the lamp 1.

The lead wires 30 a and 30 b have a core 96 using a copper wire, forexample, and an insulating layer 97 to cover the core 96. The insulatinglayer 97 is removed at the ends of the lead wires 30 a and 30 b.Therefore, the core 96 is exposed to the outside of the insulating layer97 at the ends of the lead wires 30 a and 30 b. The exposed core 96 iselectrically connected to the wiring board 28 by means of soldering.

If the insulating layer 97 is unevenly removed, the length of the core96 exposed to the insulating layer 97 fluctuates. For example, as shownin FIG. 15, when the lead wire 30 a is guided from the through hole 33 ato the through hole 16 a, the exposed core 96 may be positioned insidethe through hole 16 a. The insulating cylinder 94 fit in the throughhole 16 a is interposed between the exposed core 96 and the through hole16 a, electrically insulating the core 96 and light source support 11.

Therefore, a short circuit between the exposed core 96 and light sourcesupport 11 can be prevented by the insulating cylinder 94.

The exposed core 96 is inserted from the insertion hole 95 into a pairof through holes 98 formed on the wiring board 19, and guided onto thewiring board 19 through the through holes 98. The end of the exposedcore 96 is soldered to a land (not shown) formed on the wiring board 19.

The wiring board 28 of the lighting circuit 5 is offset to the centerline X1 of the lamp 1 as already described. Therefore, as shown in FIG.16, each through hole 98 can be placed between the adjacent areas 23 aand 23 b, and 23 c and 23 d of the thermal diffusion layer 23. This doesnot decrease the area of the thermal diffusion layer 23, though thethrough hole 98 penetrates the wiring board 19. Therefore, the heat ofthe light-emitting diodes 18 can be efficiently transmitted to the lightsource support 11 through the thermal diffusion layer 23, and preventsoverheat of the light-emitting diodes 18.

FIG. 21 to FIG. 25 shows a seventh embodiment of the invention.

A lamp 100 according to the seventh embodiment has an outer shell 101, alight source 102, a light source cover 103, a cover holder 104, alighting circuit 105, an insulating member 106, a base 107, and a heatshielding cover 108.

The outer shell 101 is made of metal material with excellent heatconductivity, such as aluminum. As shown in FIG. 24, the outer shell 101has a peripheral wall 110 and an end wall 111. The peripheral wall 110and the end wall 111 are formed integrally. The peripheral wall 110 isshaped like a straight cylinder. The outer circumference of theperipheral wall 110 is a heat radiating surface 112.

The end wall 111 closes one end of the peripheral wall 110. The end wall111 forms a circular plate light source support 113. The light sourcesupport 113 has a flat supporting surface 114 on the opposite side ofthe peripheral wall 110.

A receptacle 116 is formed inside the outer shell 101. The receptacle116 is defined by a space surrounded by the peripheral wall 110 and endwall 111, and positioned inside the heat radiating surface 112. Astopper 117 is formed at a corner defined by the peripheral wall 110 andthe end wall 111. The stopper 117 is formed circular, projecting to theinside surface of the peripheral wall 110 and continuing in thecircumferential direction of the peripheral wall 110. The receptacle 116has an open end 116 a facing to the end wall 111. The open end 116 a ispositioned at the other end of the peripheral wall 110. An engaginggroove 118 is formed in the internal circumference of the peripheralwall 110. The engaging groove 118 is positioned at the open end 116 a ofthe receptacle 116, and formed circular continuing in thecircumferential direction of the peripheral wall 110.

A recession 119 is formed in the outer circumference of the end wall111. The recession 119 is circular surrounding the light source support113. A male screw 121 is formed in the internal circumference of therecession 119. Instead of the male screw 121, a female screw may beformed on the outer circumference of the recession 119.

As shown in FIG. 24, a pair of through holes 122 a and 122 b and a pairof projections 123 a and 123 b are formed on the supporting surface 114of the light source support 113. The through holes 122 a and 122 b arearranged with an interval in the radial direction of the light sourcesupport 113. The projections 123 a and 123 b are cylindrical, andproject vertically from the supporting surface 114. The projections 123a and 123 b are arranged with an interval in the radial direction of thelight source support 113. The arrangement direction of the through holes122 a and 122 b is orthogonal to the arrangement direction of theprojections 123 a and 123 b.

As shown in FIG. 21 and FIG. 24, the light source 102 has a base 125, awiring board 126, and a chip-shaped light-emitting element 127. The base125 is made of metal material with excellent heat conductivity, such asan aluminum alloy. The wiring board 126 is stacked on the base 125. Thelight-emitting element 127 is a light-emitting diode, for example, andmounted at the center of the wiring board 126.

The light-emitting element 127 is covered by a transparent semisphericalprotection glass 128. The wiring board 126 has lands 129. The lands 129are arranged with an interval in the circumferential direction of thewiring board 126, just like surround the protection glass 128. Thewiring board 126 is covered by a not-shown insulating layer except theprotection glass 128 and lands 129.

As shown in FIG. 24, a pair of lead wire insertion parts 131 a and 131b, a pair of first engaging parts 132 a and 132 b, and a pair of secondengaging parts 133 a and 133 b are formed in the outer circumference ofthe base 125 and the wiring board 126. The lead wire insertion parts 131a and 131 b, first engaging parts 132 a and 132 b, and second engagingparts 133 a and 133 b are U-shaped notches. The lead wire insertionparts 131 a and 131 b, the first engaging parts 132 a and 132 b, and thesecond engaging parts 133 a and 133 b are not limited to the notches.They may be circular holes, for example.

The lead wire insertion parts 131 a and 131 b, the first engaging parts132 a and 132 b, and the second engaging parts 133 a and 133 b arealternately arranged with an interval in the circumferential directionof the base 125 and wiring board 126. In other words, the lead wireinsertion parts 131 a and 131 b, the first engaging parts 132 a and 132b, and the second engaging parts 133 a and 133 b are positioned amongthe adjacent lands 129.

As shown in FIG. 21 and FIG. 22, the base 125 of the light source 102 isstacked on the supporting surface 114 of the light source support 113. Aheat conduction sheet 135 having elasticity is interposed between thesupporting surface 114 of the light source support 113 and the base 125.The heat conduction sheet 135 is made of resin composed mainly ofsilicon, for example, and formed circular one size larger than the lightsource 102. The heat conduction sheet 135 thermally connects the base125 of the light source 102 and the light source support 113.

The heat conduction sheet 135 has escapes 136 a, 136 b, 136 c, 136 d,136 e and 136 f on the periphery with an interval. The escapes 136 a,136 b, 136 c, 136 d, 136 e and 136 f are U-shaped notches, for example.The escape 136 a and 136 b correspond to the lead wire insertion parts131 a and 131 b. The escapes 136 c and 136 d correspond to the firstengaging parts 132 a and 132 b. The escapes 136 e and 136 f correspondto the second engaging parts 133 a and 133 b.

In the state that the heat conduction sheet 135 is held between thelight source support 113 and base 125, the projections 123 a and 123 bprojecting from the supporting surface 114 are tightly fit in the firstengaging parts 132 a and 132 b through the escapes 136 c and 136 d ofthe heat conduction sheet 135. This fitting prevents movement of thelight source 102 in the circumferential and radial directions of thelight source support 113. As a result, the light-emitting element 127 ispositioned on the center line of the outer shell 101, and the lead wireinsertion parts 131 a and 131 b are aligned with the escapes 136 a and136 b.

As shown in FIG. 21 and FIG. 22, the light source cover 103 has a lens138 and a lens holder 139. The lens 138 is used to control luminousintensity distribution of the lamp 101, and is formed as one boy made oftransparent material, such as glass and synthetic resin.

The lens 138 has a light reflecting plane 140, a light radiating plane141, a recession 142, and a flange 143. The light reflecting plane 140is spherical, for example. The light radiating plane 141 is flat andfaced to the light reflecting plane 140. The recession 142 is caved infrom the center of the light reflecting plane 140 to the light radiatingplane 141 to permit fitting-in of the protection glass 128. Therecession 142 has a light entrance plane 144 surrounding the protectionglass 128. The flange 143 projects from the outer circumference of thelens 138 to the outside of the radial direction of the lens 138. Theflange 143 adjoins the light radiating plane 141, and continues in thecircumferential direction of the lens 138.

The lens holder 139 is a part separated from the lens 138, andcylindrical surrounding the lens 138. As shown in FIG. 25, the lensholder 139 has a pair of holder elements 146 a and 146 b. The holderelements 146 a and 146 b are made of non-translucent synthetic resinmaterial having electrical insulation, and formed semi-cylindrical.

The holder elements 146 a and 146 b have a pair of projections 147 a and147 b and a pair of recessions 148 a and 148 b. The projections 147 aand 147 b of one holder element 146 a fit in the recessions 148 a and148 b of the other holder element 146 b. The projections 147 a and 147 bof the other holder element 146 b fit in the recessions 148 a and 148 bof one holder element 146 a. By this fitting, the holder elements 146 aand 146 b are butted against each other, and assembled as thecylindrical lens holder 139.

An engaging groove 149 is formed in the internal circumference of thelens holder 139. The engaging groove 149 is positioned at one end alongthe axial direction of the lens holder 139, and continued in thecircumferential direction of the lens holder 139. Projections 151 a and151 b paired with a receiving part 150 are formed at the other end alongthe axial direction of the lens holder 139.

The receiving part 150 faces to the outer circumference of the wiringboard 126 of the light source 102, and has notches 152. The notches 152are arranged with an interval in the circumferential direction of thelens holder 139, so as to correspond to the lands 129 of the lightsource 102. The projections 151 a and 151 b correspond to the secondengaging parts 133 a and 133 b of the light source 102, and project fromthe other end of the lens holder 139 to the light source 102.

As shown in FIG, 25, the holder elements 146 a and 146 b are buttedagainst each other with the lens 138 interposed therebetween. By thisarrangement, the flange 143 of the lens 138 is fit in the engaginggroove 149, and held between the holder elements 146 a and 146 b. As aresult, the lens 138 is held inside the lens holder 139, and the lightradiating plane 141 of the lens 138 closes one end of the lens holder139.

As shown in FIG. 21 and FIG. 22, the light source 102 is held betweenthe light source cover 103 and the light source support 113 of the outershell 101. Specifically, the receiving part 150 of the lens holder 139contacts the wiring board 126 of the light source 102, just likeavoiding the lands 129. Further, the projections 151 a and 151 bprojecting from the lens holder 139 fit tightly in the second engagingparts 133 a and 133 b of the light source 102. This fitting preventsmovement of the light source cover 103 in the circumferential and radialdirections of the light source 102. Therefore, the protection glass 128covering the light-emitting element 127 fits in the recession 142 of thelens 138, and the lead wire insertion parts 131 a and 131 b or the firstengaging parts 132 a and 132 b engage with the notches 152 of thereceiving part 150.

Therefore, the position of the light source cover 103 is determined tothe light source 102, so that the optical axis X2 of the lens 138 shownin FIG. 21 is aligned with the light-emitting element 127.

As shown in FIG. 21, the cover holder 104 is formed as a cylinder or asquare cylinder made of metal material with excellent heat conductivity,such as an aluminum alloy. The cover holder 104 has the same outsidediameter of the outer shell 101, and the inside diameter and lengthcapable of covering the light source 102 and light source cover 103continuously.

A pressing part 155 is formed at one end of the cover holder 104. Thepressing part 155 is a flange projecting from the internal circumferenceto the inside of the radial direction of the cover holder 104. Acircular connecting part 156 is formed coaxially at the other end of thecover holder 104. The connecting part 156 projects from the other end ofthe cover holder 104 to the recession 119 of the outer shell 101. Theconnecting part 156 has a diameter smaller than the cover holder 104. Astep 157 is formed in the boundary between the connecting part 156 andthe other end of the cover holder 104. The step 157 has a flat surfacecontinued to the circumferential direction of the cover holder 104.

A female screw 158 is formed in the internal circumference of theconnecting part 156. The female screw 158 can be fit over the male screw121 of the recession 119. If a female screw is formed in the outercircumference of the recession 119 instead of the male screw 121, a malescrew may be formed in the outer circumference of the connecting part156.

The cover holder 104 is connected coaxially with the outer shell 101 byfitting the female screw 158 over the male screw 121 of the recession119. As the cover holder 104 is connected, the pressing part 155 of thecover holder 104 butts against one end of the lens holder 139. The lensholder 139 is pressed to the light source support 113 of the outer shell102. Therefore, the light source cover 103 is held between the pressingpart 155 of the cover holder 104 and the light source 102.

As shown in FIG. 21 and FIG. 22, when the cover holder 104 is connectedto the outer shell 102, the outer circumference of the end wall 111 ofthe outer shell 102 butts against the step 157 of the cover holder 104.This increases the contacting area of the outer shell 102 and the coverholder 104, and increases a heat conduction path from the outer shell102 to the cover holder 104.

The lighting circuit 105 is used to light the light-emitting element127, and contained in the receptacle 116 of the outer shell 102. As thelighting circuit 105 is installed inside he outer shell 101, it isunnecessary to arrange the outer shell 101 and lighting circuit 105 inthe axial direction of the lamp 100. Therefore, the length of the lamp100 in the axial direction can be reduced, and the compact lamp 100 canbe provided.

As shown in FIG. 21, the lighting circuit 105 has a wiring board 160 andcircuit components 161. The lighting circuit 105 is electricallyconnected to the light source 102 through two lead wires 162 and 162 bshown in FIG. 24. The lead wires 162 a and 162 b are guided onto thewiring board 126 of the light source 102 through the lead wire insertionparts 131 a and 131 b of the light source 102 from the through holes 122a and 122 b of the light source support 113. The ends of the lead wires162 a and 162 b are soldered to the two lands 129. The insulating member106 is an example of an insulating layer for electrically insulating theouter shell 101 and the lighting circuit 105. The insulating member 106is a molding using synthetic resin material such as polybutyleneterephthalate. As shown in FIG. 21, the insulating member 106 iscup-shaped having a cylindrical peripheral wall 163 a and a closed wall163 b closing one end of the peripheral wall 163 a.

The insulating member 106 is fit in the receptacle 116 through the openend 116 a. Therefore, the peripheral wall 163 a of the insulating member116 butts contacts the internal circumference of the peripheral wall 110of the outer shell 101, and the closed wall 163 b of the insulatingmember 116 butts against the stopper 117. The stopper 117 is interposedbetween the light source support 113 and the closed wall 163 b of theinsulating member 116. Therefore, the light source support 113 andclosed wall 163 b are separated, and a gap 165 is provided between them.

The existence of the gap 165 keeps the light source support 113thermally connected to the light source 102 non-contacting with theinsulating member 106. The gap 165 functions as a heat shielding spaceto prevent conduction of heat from the light source support 113 to theinsulating member 106, and the heat of the light source 102 is difficultto transmit directly from the light source support 113 to the insulatingmember 106.

Therefore, though the lighting circuit 105 is contained in the outershell 101 which receives the heat of the light source 102, the lightingcircuit 105 can be protected against the heat of the light source 102.This prevents a malfunction of the lighting circuit 105, and makes thelife of the lighting circuit 105 long.

The closed wall 163 b of the insulating member 106 has a not-shown pairof through holes. The through holes are formed to pass the lead wires162 a and 162 b, and opened to the receptacle 116 and the gap 165,penetrating the closed wall 163 b.

The base 107 is used to supply an electric current to the lightingcircuit 105. The base 107 has a metal base shell 167 and a connectingmember 168 fixed to the base shell 167. The base shell 167 is removablyconnected to a lamp socket of a light fixture. The lamp 100 of theseventh embodiment is configured to be fit to a lamp socket with thebase 107 faced up as shown in FIG. 21.

The connecting member 168 is a molding using synthetic resin materialsuch as polybutylene terephthalate. The connecting member 168 haselectrical insulation, and heat conductivity lower than the outer shell101.

The connecting member 168 has a distal end 169 fit inside the open end116 a of the receptacle 116. An engaging projection 170 is formed in theouter circumference of the distal end 169. The engaging projection 170engages with the engaging groove 118 when the distal end 169 is fitinside the open end 116 a. By this engagement, the outer shell 101 andthe base 107 are coaxially connected. The connecting member 168 isinterposed between the base shell 167 and the outer shell 101, andinsulates them electrically and thermally.

As shown in FIG. 21, the connecting member 168 has an outercircumference 171 larger than the diameter of the distal end 169. Theouter circumference 171 projects coaxially to the outside of the radialdirection of the outer shell 101. A circular supporting wall 172 isformed in the outer circumference 171 of the connecting member 168. Thesupporting wall 172 coaxially surrounds the distal end 169 of theconnecting member 168. A male screw 173 is formed on the outerperipheral surface of the supporting wall 172.

The heat shielding cover 108 is a molding using synthetic resinmaterial, and formed like a hollow cylinder. The heat shielding cover108 has heat conductivity lower than the outer shell 101. As shown inFIG. 21, the heat shielding cover 108 has the inside diameter and lengthcapable of coaxially surrounding the outer shell 101 and cover holder104.

A female screw 174 is formed in the internal circumference of one end ofthe heat shielding cover 108. An engaging part 175 is formed at theother end of the heat shielding cover 108. The engaging part 175 is aflange projecting from the internal circumference of the other end ofthe heat shielding cover 108 to the inside of the radial direction. Theinside diameter of the engaging part 175 is smaller than the outsidediameter of the cover holder 104.

The female screw 174 of the heat shielding cover 108 is fit over themale screw 173 of the connecting member 168. By this fitting, theengaging part 175 of the heat shielding cover 108 is caught by one endof the cover holder 104. Therefore, the cover 108 is connected to theconnecting member 168 of the base 107, surrounding the outer shell 101and cover holder 104 coaxially.

A heat radiating path 176 is formed between the heat shielding cover 108and the outer shell 101, and between the heat shielding cover 108 andthe cover holder 140. The heat radiating path 176 surrounds the outershell 101 and cover holder 104, and continues in the radial direction ofthe lamp 100.

One end of the heat radiating path 176 is closed by the outercircumference 171 of the connecting member 168. Exhaust ports 177 areformed in the outer circumference 171 of the connecting member 168. Theexhaust ports 177 are arranged with an interval in the circumferentialdirection of the connecting member 168, and connected to one end of theheat radiating path 176. The other end of the heat radiating path 176 isclosed by the engaging part 175 of the heat shielding cover 108. Suctionports 178 are formed in the engaging part 175 of the heat shieldingcover 108. The suction ports 178 are arranged with an interval in thecircumferential direction of the heat shielding cover 108, and connectedto the other end of the heat radiating path 176.

In the seventh embodiment, the suction ports 178 are formed in theengaging part 175 of the heat shielding cover 108. Instead of thesuction ports 178, projections contacting one end of the cover holder104 may be formed at the other end of the heat shielding cover 108, andgaps between adjacent projections may be used as suction ports.Similarly, through holes opened to the heat radiating path 176 may beformed at the other end of the heat shielding cover 108, and used assuction ports.

Further, instead of forming the exhaust ports 177 in the base 107,through holes opened to the heat radiating path 176 may be formed at oneend of the heat shielding cover 108, and used as exhaust ports.

Next, explanation will be given on a procedure of assembling the lamp100.

First, fit the insulating member 106 in the receptacle 116 of the outershell 101, and install the lighting circuit 105 in the receptacle 116covered by the insulating member 106. Next, guide the two lead wires 162a and 162 b extending from the light circuit 105, to the through holes122 a and 122 b of the light source support 113 through the throughholes of the closed wall 163 b.

Then, place the heat conduction sheet 135 on the supporting surface 114of the light source support 113, and stack the base 125 of the lightsource 102 on the heat conduction sheet 135. In this time, fit theprojections 123 a and 123 b of the light source support 113 in the firstengaging parts 132 a and 132 b of the light source 102 through theescapes 136 c and 136 d of the heat conduction sheet 135. This fittingdetermines the relative positions of the light source 102 and the lightsource support 113. Guide the lead wires 162 a and 162 b from thethrough holes 122 a and 122 b to the adjacent two lands 129 through thelead wire insertion parts 131 a and 131 b of the light source 102, andsolder the lead wires 162 a and 162 b to the lands 129.

Next, place the light source cover 103 on the wiring board 126 of thelight source 102. In this time, fit the projections 151 a and 151 bprojected from the lens holder 139, in the second engaging parts 133 aand 133 b of the light source 102. This fitting determines the relativepositions of the light source 102 and the light source support 103.Therefore, the optical axis X2 of the lens 138 coincides with the centerof the light-emitting element 127, and the receiving part 150 of thelens holder 139 butts against the outer circumference of the wiringboard 126.

Next, insert the female screw 158 of the cover holder 104 onto the malescrew 121 of the outer shell 102, and connect the cover holder 104coaxially with the outer shell 101. As the cover holder 104 isconnected, the pressing part 155 of the cover holder 104 butts againstone end of the lens holder 139, and presses the lens holder 139 towardthe light source support 113. As a result, the light source 102 ispressed to the supporting surface 114 of the light source support 113through the lens holder 139, and the heat conduction sheet 135 istightly held between the supporting surface 114 and the base 125 of thelight source 102.

The heat conduction sheet 135 is elastically deformed and tightly stuckto the supporting surface 114 and the base 125. This eliminates a gapbetween the supporting surface 114 and the base 125 disturbing theconduction of heat, and provides good conduction of heat between thesupporting surface 114 and the base 125. In other words, comparing thecase that the heat conduction sheet 135 is not used, the heat conductionperformance from the light source 102 to the light source support 113 isimproved.

At the same time, the engagement of the male and female screws 121 and158 is made tight by a repulsive force of the heat conduction sheet 135to elastically return to the original form. Therefore, the cover holder104 is difficult to become loose.

For example, when the accuracy of the supporting surface 114 and base125 is high, the heat conduction sheet 135 can be omitted. Instead ofthe heat conduction sheet 135, conductive grease composed mainly ofsilicon may be used.

When the light source 102 is pressed to the light source support 113, arevolving force generated by insertion of the cover holder 104 acts onthe light source cover 103 and light source 102. As already explained,the relative position of the light source 102 to the light sourcesupport 113 is determined by the fitting of the projections 123 a and123 b with the first engaging parts 132 a and 132 b. Similarly, therelative position of the light source cover 103 to the light source 102is determined by the fitting of the projections 151 a and 151 b with thesecond engaging parts 133 a and 133 b.

Therefore, the light source cover 103 and the light source 102 do notrotate following the cover holder 104. An unreasonable force causing abreak and a crack is not applied to the soldered part between the lands129 of the light source 102 and the lead wires 162 a and 162 b. The lamp100 can be assembled without giving a stress to the soldered partbetween the lead wires 162 a and 162 b and the lands 129.

Next, fit the base 107 to the outer shell 101. This work is performed byfitting the distal end 169 of the base 107 in the open end 116 of theouter shell 101, and engaging the engaging projection 170 with theengaging groove 118.

When fitting the base 107 to the outer shell 101, the lighting circuit105 may receive a force of pressing to the light source support 113,from the connecting part 168 of the base 107. This force is transmittedto the light source 102 through the lead wires 162 a and 162 b.

The light source 102 is held between the light source cover 103 and thelight source support 113. Even if a force is applied to the light source102 through the lead wires 162 a and 162 b, the light source 102 willnot be separated from the supporting surface 114 of the light sourcesupport 113. Therefore, the tight contact between the light source 102and the light source support 113 is maintained, and the optical axis X2of the lens 138 will not be deviated from the center of thelight-emitting element 127.

Finally, fit the heat shielding cover 108 to the outside of the outershell 101 and the cover holder 104, and insert the female screw 174 ofthe heat shielding cover 108 onto the male screw 173 of the connectingmember 168. By the insertion, the engaging part 175 of the heatshielding cover 108 is caught by one end of the cover holder 104. As aresult, the heat shielding cover 108 is connected to the base 107,surrounding coaxially the outer shell 101 and the cover holder 104, andthe assembling of the lamp 100 is completed.

In the state that the assembling of the lamp 100 is completed, the heatradiating path 176 positioned inside the heat shielding cover 108 isopened to the atmosphere through the suction ports 178 and exhaust ports177.

In the lamp 100 of the seventh embodiment, when the lamp 100 is lit, thelight-emitting element 127 is heated. The heat of the light-emittingelement 127 is transmitted from the base 125 of the light source 102 tothe light source support 113 through the heat conduction sheet 135. Theheat transmitted to the light source support 113 is transmitted to theheat radiating surface 112 from the end wall 110 through the peripheralwall 110, and radiated from the heat radiating surface 112 to the heatradiating path 176.

The light source support 113 receiving the heat of the light-emittingelement 127 is formed integrally with the peripheral wall 110 having theheat radiating surface 112, and there is no joint disturbing theconduction of heat in a heat conduction path from the light sourcesupport 113 to the radiating surface 112. Therefore, the thermalresistance of the heat conduction path can be controlled to small, andthe heat of the light-emitting element 127 transmitted to the lightsource support 113 can be efficiently escaped to the heat radiatingsurface 112. At the same time, as the whole surface of the heatradiating surface 112 is exposed to the heat radiating path 176, theheat radiation from the heat radiating surface 112 is not disturbed.This improves the cooling performance of the light-emitting element 27.

Further, as the metal cover holder 104 is screwed into the outer shell101, the engagement of the female screw 174 and the male screw 173thermally connects the outer shell 101 and the cover holder 104.Therefore, the heat of the outer shell 101 is transmitted also to thecover holder 104, and radiated from the outer peripheral surface of thecover holder 104 to the heat radiating path 176. Therefore, the heatradiating area of the lamp 100 can be increased by using the coverholder 104, and the cooling performance of the light-emitting element127 is improved furthermore.

When the heat of the light-emitting element 127 is radiated to the heatradiating path 176, an ascending current is generated in the heatradiating path 176. Therefore, the air outside the lamp 100 is taken inthe heat radiating path 176 through the suction ports 178 positioned atthe lower end of the lamp 100. The air taken in the heat radiating path176 flows from the lower to upper side in the heat radiating path 176,and is radiated to the atmosphere through the exhaust ports 177.

The outer circumference of the cover holder 104 and the heat radiatingsurface 112 of the outer shell 101 are exposed to the heat radiatingpath 176. The heat of the light-emitting element 127 transmitted to thecover holder 104 and the outer shell 101 is taken away by the heatexchange with the air flowing in the heat radiating path 176. Therefore,the cover holder 104 and the outer shell 101 can be cooled by the air,and overheat of the light-emitting element 127 can be prevented. Thisprevents decrease of the light-emitting efficiency of the light emittingelement 127, and makes the life of the light-emitting element 127 long.

The heat shielding cover 108 to cover the cover holder 104 and the outershell 101 is made of synthetic resin material with a low heatconductivity. Therefore, the heat of the cover holder 104 and the outershell 101 is difficult to transmit to the heat shielding cover 108, andthe temperature of the heat shielding cover 108 is decreased to lowerthan the outer shell 101.

According to the seventh embodiment, the connecting member 168 to fitwith the heat shielding cover 108 is made of synthetic resin, and theconnecting member 168 thermally insulates the outer shell 101 and theheat shielding cover 108. Further, the engaging part 175 of the heatshielding cover 108 to contact the cover holder 104 has the suctionports 178. Even if the heat of the cover holder 104 is transmitted tothe engaging part 175 of the heat insulating cover 108, the engagingpart 175 is cooled by the air flowing into the heat radiating path 176through the suction ports 178. Therefore, the heat shielding cover 108is difficult to be influenced by the heat of the cover holder 104, andthe temperature increase of the heat shielding cover 108 can beprevented.

According to the lamp 100 of the seventh embodiment, even if theoperator holds the heat insulating cover 108 by hand when replacing thelamp 100 during lighting or immediately after turning off the lamp, theoperator does not feel hot. Therefore, the operator does not drop thelamp 100 when touching the lamp and surprised by the heat, and cansafely replace the lamp 100.

In the seventh embodiment, fine holes may be formed in the heatinsulating cover 108. Instead of holes, slits may be formed along theaxial or circumferential direction of the heat shielding cover 108.

FIG. 26 and FIG. 27 show an eighth embodiment of the invention. Theeighth embodiment is different from the seventh embodiment in theconfiguration for radiating the heat of the outer shell 101 and thecover holder 104. The other components of the lamp 100 and technicaleffects are the same as those of the seventh embodiment. Therefore, thesame components as those of the seventh embodiment are given samereference numerals, and explanation of these components will be omitted.

The lamp 100 according to the eighth embodiment has the followingconfiguration instead of the heat shielding cover 108 in the seventhembodiment. As shown in FIG. 26 and FIG. 27, the outer shell 101 hasfirst heat radiating fins 200. The first heat radiating fins 200 projectradially from the heat radiating surface 112 of the outer shell 101. Thefirst heat radiating fins 200 are extended in the axial direction of theouter shell 101, and arranged with an interval in the circumferentialdirection of the outer shell 101.

The cover holder 104 has second heat radiating fins 201. The second heatradiating fins 201 project radially from the outer circumference of thecover holder 104. The second heat radiating fins 201 are extend in theaxial direction of the cover holder 104, and arranged with an intervalin the circumferential direction of the cover holder 104.

The first and second heat radiating fins 200 and 201 continue each otheralong the axial direction of the lamp 100. Therefore, the first andsecond heat radiating fans 200 and 201 are thermally connected, anddirectly exposed to the outside of the lamp 100.

The distal edges of the first heat radiating fins 200 are covered byfirst edge covers 202. Similarly, the distal edges of the second heatradiating fins 201 are covered by second edge covers 203. The first andsecond edge covers 202 and 203 are mode of synthetic resin. The firstand second edge covers 202 and 203 have heat conductivity lower than theouter shell 101 and the cover holder 104.

According to the lamp 100 of the eighth embodiment, the existence of thefirst heat radiating fins 200 increase the heat radiating area of theheat radiating surface 112 of the outer shell 101. Likewise, theexistence of the second heat radiating fins 201 increases the heatradiating area of the peripheral surface of the cover holder 104.Therefore, the heat of the light-emitting element 127 transmitted to theouter shell 101 and the cover holder 104 can be efficiently radiated tothe outside of the lamp 100. This can prevent the decrease of thelight-emitting efficiency of the light-emitting element 127, and makethe life of the light-emitting element 127 long.

Further, the first and second edge covers 202 and 203 covering thedistal edges of the first and second heat radiating fins 200 and 201have heat conductivity lower than the outer shell 101 and the coverholder 104. Therefore, the heat of the outer shell 101 and the coverholder 104 is difficult to transmit to the first and second edge covers202 and 203, and the temperatures of the first and second edge covers202 and 203 can be decreased to lower than the outer shell 101 and thecover holder 104.

As a result, even if the operator holds the first and second heatradiating fins 200 and 201 by hand when replacing the lamp 100 duringlighting or immediately after turning off the lamp, the operator doesnot feel hot. Therefore, the operator does not drop the lamp 100 whentouching the lamp and surprised by the heat, and can safely replace thelamp 100.

FIG. 28 and FIG. 29 show a ninth embodiment of the invention.

The ninth embodiment is developed from the eight embodiment. Theconfiguration of the lamp 100 is the same as the eight embodiment.Therefore, the same components as those of the eighth embodiment aregiven same reference numerals, and explanation of these components willbe omitted.

The lamp 100 of the ninth embodiment has an outside cylinder 220surrounding the first and second heat radiating fins 200 and 201. Theoutside cylinder 220 is formed like a hollow cylinder with the diameterlarger than the outer shell 101 and the cover holder 104. The outsidecylinder 220 has the length extending over the peripheral wall 110 ofthe outer shell 101 and the cover holder 104. The inner peripheralsurface of the outside cylinder 220 contacts the first and second edgecovers 202 and 203. Therefore, the outside cylinder 220 extends over theadjacent first and second heat radiating fins 200 and 201.

In other words, the outside cylinder 220 faces to the heat radiatingsurface 112 through the first heat radiating fins 200, and faces to theperipheral surface of the cover holder 104 through the second heatradiating fins 201. Therefore, a heat radiating path 221 is formedbetween the heat radiating surface 112 of the outer shell 101 and theoutside cylinder 220, and between the peripheral surface of the coverholder 104 and the outside cylinder 220. The heat radiating path 221continues in the axial direction of the lamp 100. The first and secondheat radiating fins 200 and 201 are exposed to the heat radiating path221. The heat radiating path 221 has one end 221 a and the other end 221b. The one end 221 a of the heat radiating path 221 is opened to theatmosphere from the lower end of the second heat radiating fins 201,when the lamp 100 is lit with the base 107 faced up. Likewise, the otherend 221 b of the heat radiating path 221 is opened to the atmospherefrom the upper end of the first heat radiating fins 200, when the lamp100 is lit with the base 107 faced up.

The outside cylinder 220 is made of material with heat conductivitylower than the outer shell 101 and the cover holder 104. For example,when the outside cylinder 220 is made of heat shrinking synthetic resin,it is desirable to heat the outside cylinder 220 to shrink by the heat,after fitting the outside cylinder 222 to the outside of the outer shell101 and the cover holder 104. The inner circumference of the outsidecylinder 220 is pressed to the first and second edge covers 202 and 203,and the outside cylinder 220 is connected integrally with the outershell 101 and the cover holder 104. This facilitates fitting of theoutside cylinder 220.

In the lamp 100 of the ninth embodiment, when the heat of thelight-emitting element 127 is radiated to the heat radiating path 221,an ascending current is generated in the heat radiating path 221.Therefore, the air outside the lamp 100 is taken in the heat radiatingpath 221 through one end 221 a of the heat radiating path 221. The airtaken in the heat radiating path 221 flows from the lower to upper sidein the heat radiating path 221, and is radiated to the atmospherethrough the other end 221 b of the heat radiating path 221.

The heat of the light-emitting element 127 transmitted to the coverholder 104 and the outer shell 101 is taken away by the heat exchangewith the air flowing in the heat radiating path 221. Therefore, theouter shell 101 having the first heat radiating fins 200 and the coverholder 104 having the second heat radiating fins 201 can be cooled bythe air, and overheat of the light-emitting element 127 can beprevented. This prevents decrease of the light-emitting efficiency ofthe light emitting element 127, and makes the life of the light-emittingelement 127 long.

The outside cylinder 220 is made of synthetic resin material with theheat conductivity lower than the outer shell 101 and the cover holder104. Therefore, the heat of the cover holder 104 and the outer shell 101is difficult to transmit to the outside cylinder 220, and thetemperature of the outside cylinder 220 is decreased to lower than theouter shell 101 and the cover holder 104.

As a result, even if the operator holds the outside cylinder 220 by handwhen replacing the lamp 100 during lighting or immediately after turningoff the lamp, the operator does not feel hot. Therefore, the operatordoes not drop the lamp 100 when touching the lamp and surprised by theheat, and can safely replace the lamp 100.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details and representative embodiments shownand described herein. Accordingly, various modifications may be madewithout departing from the spirit or scope of the general inventiveconcept as defined by the appended claims and their equivalents.

1. A lamp comprising: an outer shell which includes a light sourcesupport; a base which is provided in the outer shell; a board which isfixed to the light source support through a screw, the screw comprisinga head which projects from the board; a plurality of light-emittingelements mounted on the board, the light-emitting elements projectingfrom the board in a same direction as the head of the screw, and heightof projection of the light-emitting elements with respect to the boardbeing almost same as height of projection of the head with respect tothe board; and a translucent cover which covers the board, the head ofthe screw, and the light-emitting elements, the translucent covercomprising an edge held by the outer shell, and a semi-spherical areawhich projects beyond the head of the screw and the light-emittingelements to an opposite side of the outer shell with respect to theedge, and transmits light emitted by the light-emitting element.
 2. Thelamp of claim 1, wherein the screw is positioned in the center of theboard and is surrounded by the light-emitting element.
 3. The lamp ofclaim 1, wherein the translucent cover comprises at one end thereof anopening defined by the edge, and the board is positioned inside theopening of the translucent cover.
 4. The lamp of claim 3, wherein thetranslucent cover comprises a top portion which faces the opening, andthe semi-spherical area includes the top portion.
 5. The lamp of claim4, wherein the light source support comprises a projection placed insidethe semi-spherical area of the translucent cover.
 6. The lamp of claim5, wherein the projection has a distal end surface exposed to the insideof the semi-spherical area, and the board is provided on the distal endsurface.